Poly(Ionic Liquid) Sorbents and Membranes for CO2 Separation

ABSTRACT

Polymerizable ionic liquid monomers and their corresponding polymers (poly(ionic liquid)s) are created and found to exhibit high CO 2  sorption. The poly(ionic liquid)s have enhanced and reproducible CO 2  sorption capacities and sorption/desorption rates relative to room-temperature ionic liquids. Furthermore, these materials exhibit selectivity relative to other gases such as nitrogen, methane, and oxygen. They are useful as efficient separation agents, such sorbents and membranes. Novel free-radical and condensation polymerization approaches are used in the preparation of the poly(ionic liquids).

This application is a divisional application of U.S. patent applicationSer. No. 11/659,484, filed Dec. 11, 2008, which was a National Stageapplication of PCT/US2005/027833, which claims priority to U.S. PatentApplication Ser. No. 60/599,188, filed Aug. 5, 2004.

BACKGROUND OF THE INVENTION

The invention relates generally to novel materials, namely polymers madefrom ionic liquids, referred to herein as poly(ionic liquid)s, and, morespecifically, to poly(ionic liquid)s for absorbing carbon dioxide (CO₂).

Global warming resulting from the increased CO₂ concentration in theatmosphere due to emissions of CO₂ from fossil fuel combustion isbecoming one of most important environmental issues.^(1,2) Recently, CO₂capture and sequestration are receiving significant attention. Forcarbon sequestration, because the cost of capture and separation areestimated to make up three-fourths of total costs of ocean or geologicsequestration, it is important to develop new materials and methods toseparate and capture CO₂ from flue gas^(3,4,5) and other gas mixtures.

Ionic liquids, which are organic salts that become liquids usually belowabout 200° C., have attracted attention because of their unique chemicaland physical properties and wide application potentials.⁶⁻¹² Recently,CO₂ was found to be remarkably soluble in ionic liquids, and thus ionicliquids have been explored as non-volatile, and reversible absorbentsfor CO₂ separation.¹³⁻²¹ For instance, at 15 bar of CO₂ pressure, theCO₂ solubility in 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF₆]) is about 23 mol. %.¹⁹ The CO₂ solubility in the ionicliquids is dependent on their cations and substituents, and especiallyon their anions.¹⁹ For example, fluorine-containing anions (e.g.bis(trifluoromethyl-sulfonyl)imide, Tf₂N),¹⁹ or cations,²² or aminegroups²³ tend to increase the CO₂ solubility. Ionic liquids have alsobeen impregnated into porous materials for developing supported liquidmembranes. Such membranes have high CO₂ selectivity and permeancebecause of the selective sorption of CO₂ in ionic liquids.²⁴⁻²⁶

We have found that poly(ionic liquid)s, the polymers prepared from ionicliquid monomers, have higher CO₂ sorption capacity than room temperatureionic liquids. Most importantly, the CO₂ sorption and desorption of thepolymers are much faster than those of ionic liquids and thesorption/desorption is completely reversible. These poly(ionic liquid)sare thus promising as sorbent and membrane materials for CO₂ separation.

SUMMARY OF THE INVENTION

The invention consists of a class of new materials consisting ofpolymers made from ionic liquids. The poly(ionic liquid)s arepolymerized ionic liquid monomers and have been found to have a CO₂absorption rate and/or a CO₂ absorption capacity higher than that of theionic liquid monomer. Certain of the poly(ionic liquid)s have a CO₂absorption capacity almost ten times that of the ionic liquid monomerfrom which they are made. The sorption/desorption rates of thepoly(ionic liquid)s are much faster than those of the correspondingionic liquid monomers, and the poly(ionic liquid)s retain theirsorption/desorption properties after going through sorption/desorptioncycling. The polymers are made primarily through free radicalpolymerization, but other methods of polymerization may also be used.

The ionic liquid monomers include: (a) Imidazolium-based ionic liquids,such as (a) 1-[2-(methacryloyloxy)ethyl]-3-butyl-imidazoliumtetrafluoroborate ([MABI][BF₄]), 1-(p-vinylbenzyl)-3-butyl-imidazoliumtetrafluoroborate ([VBBI][BF₄]), 1-(p-vinylbenzyl)-3-methyl-imidazoliumtetrafluoroborate [VBMI][BF₄], 1-(p-vinylbenzyl)-3-butyl-imidazoliumhexafluorophosphate [VBBI][PF₆], 1-(p-vinylbenzyl)-3-butyl-imidazoliumo-benzoic sulphimide ([VBBI][Sac]),1-(p-vinylbenzyl)-3-butyl-imidazolium trifluoromethanesulfonamide([VBBI][BF₄]), and (1-butylimidazolium-3)methyl-ethyleneoxide ([BIEO][BF₄]); (b) Ammonium-based ionic liquids, such as(p-vinylbenzyl)trimethyl ammonium tetrafluoroborate ([VBTMA][BF₄]),(p-vinylbenzyl)triethyl ammonium tetrafluoroborate ([VBTEA][BF₄]),(p-vinylbenzyl)tributyl ammonium tetrafluoroborate ([VBTBA][BF₄]),2-(methacryloyloxy)ethyltrimethylamnonium tetrafluoroborate([MATMA][BF₄]), (p-vinylbenzyl)trimethyl ammonium hexafluorophosphate([VBTMA][PF₆]), (p-vinylbenzyl)trimethyl ammonium o-benzoic sulphimide([VBTMA][Sac]), and (p-vinylbenzyl)trimethyl ammonium trifluoromethanesulfonamide ([VBTMA][Tf₂N]); (c) Phosphonium-based ionic liquids, suchas (p-vinylbenzyl)triethyl phosphonium tetrafluoroborate ([VBTEP][BF₄]),and (p-vinylbenzyl)triphenyl phosphonium tetrafluoroborate([VBTPP][BF₄]); (d) Pyridinium-based ionic liquids, such as1-(p-vinylbenzyl)pyridinium tetrafluoroborate ([VBP][BF₄]); and (e)Condensation polymerization ionic monomers, such asbis(2-hydroxyethyl)dimethyl ammonium tetrafluoroborate ([BHEDMA][BF₄]),2,2-bis(methylimidazolium methyl)-1,3-propanediol tetrafluoroborate([BMIMP][BF₄]), and 2,2-bis(butylimidazolium methyl)-1,3-propanedioltetrafluoroborate ([BBIMP][BF₄]).

The invention also consists of a process for the separation and recoveryof CO₂, including the steps of contacting a CO₂-containing gas mixturewith a solid sorbent that includes at least one poly(ionic liquid)compound under such conditions as to obtain a gas product having a lowerconcentration of CO₂ than the initial gas mixture and a solid sorbentcontaining absorbed carbon dioxide which has been removed from said gasmixture. Preferably, the solid sorbent is treated under conditions as tosubstantially desorb the CO₂ contained in the solid sorbent so as toobtain a regenerated solid sorbent.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graphical representation of the CO₂ sorption of thepoly(ionic liquids)s (P[VBBI][BF₄](a), P[VBBI][Tf₂N](b),P[MABI][BF₄](c), P[VBBI][Sac](d)), with their corresponding monomers([VBBI][Tf₂N](e), [MABI][BF₄](g), [VBBI][BF₄](h), [VBBI][Sac](i)), andan ionic liquid [bmim][BF₄](f) as a function of time (592.3 mmHg CO₂,22° C.).

FIG. 2 is a graphical representation of the CO₂ sorption of poly(ionicliquid)s with different polymer backbones (592.3 mmHg of CO₂ and 22°C.).

FIG. 3 is a graphical representation of the CO₂ sorption of poly(ionicliquid)s with different substituents (592.3 mmHg of CO₂ and 22° C.).

FIG. 4 is a graphical representation of the CO₂ sorption of poly(ionicliquid)s with different anions (592.3 mmHg of CO₂ and 22° C.).

FIG. 5 is a graphical representation of the gas (CO₂, O₂, N₂) sorptionof P[VBBI][BF₄] as a function of time at 592.3 mmHg, 22° C.

FIG. 6 is a graphical representation of the weight change ofP[VBBI][BF₄] (1 g) (without buoyancy correction) after introducing CO₂into the system, and then replacing CO₂ with N₂ (total pressure 592.3mmHg, 22° C.).

FIG. 7 is a graphical representation of the isothermal sorption ofP[VBBI][BF₄] and P[MABI][BF₄] at different CO₂ pressures (22° C.).

FIG. 8 is a graphical representation of the cycles of CO₂ sorption(592.3 mmHg CO₂, 22° C.) and desorption of P[VBBI][BF₄] and P[MABI][BF₄]under vacuum;

FIG. 9 is a graphical representation of CO₂ sorption (592.3 mmHg CO₂,22° C.) and desorption of a typical ionic liquid [bmim] [BF₄] undervacuum.

FIG. 10 is a graphical representation of the CO₂ sorption ofP[VBBI][BF₄] with different particle sizes (592.3 mmHg, 22° C.).

FIG. 11 is a graphical representation of the CO₂ sorption of poly(ionicliquid)s with different types of cation.

FIG. 12 is a graphical representation of the CO₂ sorption of poly(ionicliquid)s with different types of anion.

FIG. 13 is a graphical representation of the CO₂ sorption in poly(ionicliquid)s with different backbones

FIG. 14 is a graphical representation of the CO₂ sorption in poly(ionicliquid)s with different substituents.

FIG. 15 is a graphical representation of the effect of crosslinking onCO₂ sorption in poly(ionic liquid)s.

FIG. 16 is a graphical representation of the CO₂/CH₄ selectivity forP[VBTMA][BF₄]-g-PEG and P[MATMA][BF₄]-g-PEG

FIG. 17 is a graphical representation of the CO₂/CH₄ selectivity forrepresentative polymers and grafted poly(ionic liquids) (♦:representative polymers; : P[MATMA][BF₄]-g-PEG at 35° C., 50° C. and70° C.; ▴: P[VBTMA][BF₄]-g-PEG at 35° C., 50° C. and 70° C.)

FIG. 18 is a graphical representation of the CO₂/N₂ selectivity forP[VBTMA][BF₄]-g-PEG and P[MATMA][BF₄]-g-PEG

FIG. 19 is a graphical representation of the CO₂/N₂ selectivity forrepresentative polymers and grafted poly(ionic liquids) (♦:representative polymers; : P[MATMA][BF₄]-g-PEG at 35° C., 50° C. and70° C.; ▴: P[VBTMA][BF₄]-g-PEG at 35° C., 50° C. and 70° C.)

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In this description, each material is introduced by its full chemicalname followed by a shortened name in parenthesis, for example,1-[2-(methacryloyloxy)ethyl]-3-butyl-imidazolium tetrafluoroborate([MABI][BF₄]). Following the initial introduction, only the shortenedname is used.

Ionic liquids are organic salts with melting points usually below 200°C., often below room temperature. They can be substitutes for thetraditional organic solvents in chemical reactions. The most commonexamples are imidazolium and pyridinium derivatives, but phosphonium ortetralkylammonium compounds have also been explored. Specific examplesof ionic liquid monomers used for polymer synthesis and otherapplications include but are not limited to:

(1) Ionic liquid monomers based on imidazolium, such as1-[2-(methacryloyloxy)ethyl]-3-butyl-imidazolium tetrafluoroborate([MABI][BF₄]), 1-(p-vinylbenzyl)-3-butyl-imidazolium tetrafluoroborate([VBBI][BF₄]), 1-(p-vinylbenzyl)-3-methyl-imidazolium tetrafluoroborate([VBMI][BF₄]),1-(p-vinylbenzyl)-3-butyl-imidazolium hexafluorophosphate([VBBI][PF₆]), 1-(p-vinylbenzyl)-3-butyl-imidazolium o-benzoicsulphimide ([VBBI][Sac]), 1-(p-vinylbenzyl)-3-butyl-imidazoliumtrifluoromethane sulfonamide ([VBBI][BF₄]),(1-butylimidazolium-3)methyl-ethylene oxide ([BIEO][BF₄]);

(2) Ionic liquid monomers based on ammonium, such as(p-vinylbenzyltrimethyl)ammonium tetrafluoroborate ([VBTMA][BF₄]),(p-vinylbenzyl)triethyl ammonium tetrafluoroborate ([VBTEA][BF₄]),(p-vinylbenzyl)tributyl ammonium tetrafluoroborate ([VBTBA][BF₄]),[2-(methacryloyloxy)ethyl]trimethylamnonium tetrafluoroborate([MATMA][BF₄]), (p-vinylbenzyl)trimethyl ammonium hexafluorophosphate([VBTMA][PF₆]), (p-vinylbenzyl)trimethyl ammonium o-benzoic sulphimide([VBTMA][Sac]), (p-vinylbenzyltrimethyl)ammonium trifluoromethanesulfonamide ([VBTMA][Tf₂N]);

(3) Ionic liquid monomers based on phosphonium, such as(p-vinylbenzyl)triethyl phosphonium tetrafluoroborate ([VBTEP][BF₄]),(p-vinylbenzyl)triphenyl phosphonium tetrafluoroborate ([VBTPP][BF₄]);

(4) Ionic liquid monomers based on pyridinium, such as1-(p-vinylbenzyl)pyridinium tetrafluoroborate ([VBP][BF₄]);

(5) Ionic liquid monomers for condensation polymerization, such asbis(2-hydroxyethyl)dimethyl ammonium tetrafluoroborate ([BHEDMA][BF₄]),2,2-bis(methylimidazolium methyl)-1,3-propanediol tetrafluoroborate([BMIMP][BF₄]), and 2,2-bis(butylimidazolium methyl)-1,3-propanedioltetrafluoroborate ([BBIMP][BF₄]).

Poly(ionic liquid)s as used in this specification means polymers formedusing ionic liquids as monomers via free radical polymerization or otherkind of polymerization.

Free radical polymerization is a common and useful reaction for makingpolymers from vinyl monomers, that is, from small molecules containingcarbon-carbon double bonds. Polymers made by free radical polymerizationinclude polystyrene, poly(methyl methacrylate), poly(vinyl acetate) andbranched polyethylene. Free radical polymerization begins with amolecule called an initiator; common initiators are benzoyl peroxide or2,2′-azo-bis-isobutyrylnitrile (AIBN).

EXAMPLE 1 Materials

4-Vinylbenzyl chloride, methacryloyl chloride, 1-butylimidazole,2-bromoethanol, lithium trifluoromethane sulfonimide, potassiumhexafluorophosphate, sodium tetrafluoroborate,2,6-di-tert-butyl-4-methyl phenol (DBMP), 2,2′-azobisisobutyronitrile(AIBN), aluminum isopropoxide, epichlorohydrin, N,N-dimethylformamide(DMF), acetonitrile, and acetone were purchased from Aldrich.1-Methylimidazole, and o-benzoic sulphimide sodium salt hydrate werepurchased from Lancaster Synthesis Inc. These chemicals were usedwithout further purification.

Synthesis and Characterization

1-[2-(Methylacryloyloxy)ethyl]-3-butyl-imidazolium tetrafluoroborate([MABI][BF₄]) and 1-(p-vinylbenzyl)-3-butyl-imidazoliumtetrafluoroborate ([VBBI][BF₄]) were synthesized according to ourpublished reports,^(27,28) as shown in Schemes 1 and 2.1-(p-Vinylbenzyl)-3-butyl-imidazolium hexafluorophosphate ([VBBI][PF₆]),1-(p-vinylbenzyl)-3-butyl-imidazolium o-benzoic sulphimide([VBBI][Sac]), 1-(p-vinylbenzyl)-3-butyl-imidazolium trifluoromethanesulfonamide ([VBBI][Tf₂N]) were synthesized by a similar procedureexcept using NaPF₆, o-benzoic sulphimide sodium salt hydrate (NaSac) orlithium trifluoromethane sulfonamide (LiTf₂N) for anion exchangereactions. The yields were 93.0%, 49.6%, 39.9%, respectively.

1-(p-Vinylbenzyl)-3-methyl-imidazolium tetrafluoroborate ([VBMI][BF₄])was synthesized as follows: To a 50 ml flask, p-vinylbenzyl chloride (10ml, 0.064 mole), a small amount of DBMP, and 1-methylimdazole (5.14 ml,0.064 mole) were added and heated at 45° C. overnight. The solutionbecame gradually viscous. NaBF₄ (5.2 g, 0.47 mole) and dry acetone (30ml) were added. The mixture was stirred at room temperature. The viscousliquid dissolved gradually while a white solid precipitated. After 12 hreaction, the precipitate was removed by filtration. The solvent wasremoved under vacuum. The solid was washed with water and ether, anddried by vacuuming at room temperature, producing 14 g of white crystals(yield 76.5%).

[VBBI][BF₄]: ¹H NMR (400 MHz, DMSO-d₆, ppm): δ 9.24 (1H, s), 7.80 (2H,s), 7.51 (2H, d) 7.35 (2H, d), 6.73 (1H, m), 5.89 (1H, d) 5.27 (1H, d),5.40 (2H, s), 4.14 (2H, t), 1.78 (2H, m), 1.24 (2H, m), 0.88 (3H, t).mp: 67-68° C.

[VBBI][PF₆] ¹H NMR (400 MHz, DMSO-d₆, ppm): δ 9.22 (1H, s), 7.80 (2H,s), 7.48 (2H, d) 7.35 (2H, d), 6.73 (1H, m), 5.89(1H, d), 5.30 (1H, d),5.46 (2H, s), 4.14 (2H, t), 1.79 (2H, m), 1.22 (2H, m), 0.87 (3H, t).mp: 87-88.5° C.

[VBBI][Sac] ¹H NMR (400 MHz, DMSO-d₆, ppm) δ 9.38 (1H, s), 7.80 (2H, s)7.66 (1H, d), 7.61(1H, d), 7.59 (2H, d), 7.49 (2H, d), 7.40 (2H,d), 6.72(1H, m) 5.84 (1H, d), 5.42 (2H, s), 5.26 (2H, d) 4.16 (2H, m) 1.73 (2H,m), 1.21 (2H, m), 0.84 (3H, m). mp: −36-−38° C.

[VBBI][Tf₂N] ¹H NMR (400 MHz, DMSO-d₆, ppm): δ 8.83 (1H, s), 7.44 (2H,s), 7.34 (2H, d) 7.27 (2H, d), 6.70 (1H, m), 5.79(1H,d) 5.33 (1H, d),5.31 (2H, s), 4.17 (2H, t), 1.84 (2H, m), 1.35 (2H, m), 0.94 (3H, t).mp: −61-−62° C.

[VBMI][BF₄]: ¹H NMR (400 MHz, DMSO-d₆, ppm): 9.13 (1H, s), 7.71 (1H, s),7.63 (1H, s), 7.52 (1H, d), 7.42 (2H, d), 6.75 (1H, m), 5.88 (1H, d),5.41(2H, s), 5.26 (1H, d), 3.86 (3H, s). mp: 42-44° C.

Poly(ionic liquid)s were prepared from above ionic liquid monomers byfree radical polymerization. A typical example is as the following:[VBBI][BF₄] (3 g), AIBN (30 mg) and DMF (3 ml) were charged into areaction tube. The tube was tightly sealed, and degassed. It wasimmersed in an oil bath at 60° C. for 6 h. The solution was poured intomethanol to precipitate out the polymer. The polymer was dried undervacuum at 100° C. The yield was 2.3 g (75%).

Poly[1-(p-Vinylbenzyl)-3-butyl-imidazolium tetrafluoroborate](P[VBBI][BF₄]): ¹H NMR (DMSO-d₆, 400 MHz, ppm): δ 9.12 (s, 1H), 7.8 (br,1H), 7.4 (br, 1H),7.1 (br, 2 H), 6.4 (br, 2H), 5.6-4.9 (br, 2H), 4.1(br, 2H) , 2.1-1.0 (m, 7H), 0.8 (s, 3 H). Anal. Calcd for(C₁₆H₂₁BF₄N₂)n: C, 58.56%; H, 6.45%; N, 8.54%. Found: C, 58.35%; H,6.43%; N, 8.50%.

Poly[1-(p-Vinylbenzyl)-3-butyl-imidazolium hexafluorophosphate](P[VBBI][PF₆]): ¹H NMR (DMSO-d₆, 400 MHz, ppm): δ 9.16 (s, 1H), 7.72(br, 1H), 7.47 (br, 1H), 7.04 (br, 2H), 6.42 (br, 2H), 5.23 (br, 2H),4.15 (br, 2H) , 2.1-0.8 (m,10H) Anal. Calcd for (C₁₆H₂₁F₆N₂P)_(n): C,49.75%; H, 5.48%; N, 7.25%; Found: C, 49.70%; H, 5.37%; N, 7.12%.

Poly[1-(p-Vinylbenzyl)-3-butyl-imidazolium o-benzoic sulphimide](P[VBBI][Sac]): ¹H NMR (DMSO-d₆, 400 MHz, ppm): δ 9.44 (s, 1H), 7.5-7.9(br, 6H), 7.19 (br, 2H), 6.35 (br, 2H), 5.35 (br, 2H), 4.15 (br, 2H) ,1.9-0.5 (m,10H) Anal. Calcd for (C₂₃H₂₅N₃O₃S)_(n): C, 65.25; H, 5.91; N,9.93. Found: C, 64.11; H, 6.05; N, 9.68.

Poly[1-(p-Vinylbenzyl)-3-butyl-imidazolium trifluoromethane sulfonamide](P[VBBI][Tf₂N]): ¹H NMR (DMSO-d₆, 400 MHz, ppm): δ 9.20 (s, 1H), 7.73(br, 1H), 7.44 (br, 1H), 6.94 (br, 2 H), 6.33 (br, 2H), 5.19 (br, 2H),4.13 (br, 2H), 2.0-1.0 (m,7H), 0.81 (s, 3H). Anal. Calcd for(C₁₈H₂₁N₃F₆O₄S₂)_(n): C, 41.46; H, 4.03; N, 8.06. Found: C, 41.46; H,4.13; N, 7.94.

Poly{1-[2-(Methylacryloyloxy)ethyl]-3-butyl-imidazoliumtetrafluoroborate} (P[MABI][BF₄]): ¹H NMR (DMSO-d₆, 400 MHz, ppm): δ 9.1(br, 1H), 7.9-7.6 (d, 2H), 4.8-3.8 (m 6H), 2.0-0.2 (m, 12H). Anal. Calcdfor (C₉H₁₈BF₄NO₂)_(n): C, 48.17 H, 6.49; N, 8.65. Found: C, 47.68; H,6.48; N, 6.48.

Poly[1-(p-vinylbenzyl)-3-methyl-imidazolium tetrafluoroborate](P[VBMI][BF₄]): ¹H NMR (DMSO-d₆, 400 MHz, ppm): δ 9.10 (1H, br),7.60-7.30 (2H, br), 7.10 (2H, br), 6.40 (2H, br), 5.30(2H, br), 3.70(2H, br) 2.1˜0.5 (3H, br). Anal. Calcd for (C₁₃H₁₅BF₄N₂)_(n): C, 54.58;H, 5.25; N, 9.80. Found: C, 52.74; H, 5.33, ; N, 9.38.

The poly(ionic liquid) with poly(ethylene oxide) backbone wassynthesized from poly(epichlorohydrin) (Scheme 3). Aluminum isopropoxide(0.18 g, 0.88 mmol) was added into a 100 mL flask. The flask wasdegassed by repeated vacuum/nitrogen purging (5 cycles). Degassed THF(25 mL) and epichlorohydrin (5.0 mL, 66 mmol) was added by degassedsyringes. After the reaction flask was immersed into a 40° C. oil bathfor 12 hours, the poly(epichlorohydrin) was precipitated out by adding alarge amount of hexane. 3.3 g of poly(epichlorohydrin) was dissolved in50 mL of DMF. N-butylimidazole (5.0 g, 40 mmol) was added to the DMFsolution. This solution was stirred at 80° C. for 5 days, and then NaBF₄(4.4 g, 40 mmol) was added. After the mixture was stirred at roomtemperature for 2 days, sodium chloride precipitate was removed byfiltration. Anhydrous ethyl ether was added to the filtrate toprecipitate the poly(ionic liquid). The obtained P[BIEO][BF₄] was washedwith ethyl ether and dried in vacuum oven at 50° C. for one day. ¹H-NMR(acetone-d₆): δ 8.86 (1H, s), 7.69 (2H, br), 4.44-4.31 (4H, br), 3.97(1H, br), 3.67 (2H, br), 1.88 (2H, br), 1.34 (2H, br), 0.93 (3H, br).Anal. Calcd for (C₁₀H₁₇BF₄N₂O)_(n): C, 44.80; H, 6.34; N, 10.46. Found:C, 44.66; H, 6.26; N, 10.11.

The syntheses of ionic liquid monomers are shown in Schemes 1-3. Twosteps were generally involved in the preparations: the quaternizationreaction of 1-butylimidazole or 1-methylimidazole with 4-vinylbenzylchloride or 2-bromoethyl methacrylate, and the anion exchange reactionof the halide ions with tetrafluoroborate, hexafluorophosphate, Sac orTf₂N anions.

The quaternization with 4-vinylbenzyl chloride was fast with a highyield. The anion exchange of the resulting chloride [VBBI][Cl] and[VBMI][Cl] with BF₄ ⁻ produced the monomers, [VBBI][BF₄] and[VBMI][BF₄], as crystalline solids, which are soluble in acetone,acetonitrile, dichloromethane, DMF, and DMSO, but insoluble in diethylether. [VBBI][PF₆] is also a solid with similar solubility. [VBBI][Sac]and [VBBI][Tf₂N] are liquid at room temperature and soluble in acetone,acetonitrile, DMF, and DMSO. [VBBI][Tf₂N] is also soluble in ethylether.

The quaternization of N-butylimidazole with 2-bromoethyl methacrylatewas slow and difficult to get high yield of [MABI][Br]. After the anionexchange, [MABI][BF₄] is also a liquid at room temperature and solublein above polar solvents but insoluble in ethyl ether and other nonpolarsolvents.

All above ionic liquid monomers, unlike their corresponding chloridesalts, are insoluble in water. So unreacted chloride salts could beeasily removed by washing with water. Silver nitrate tests indicatedthat no chloride was present in all the ionic liquid monomers.

The poly(ionic liquid)s, except for P[BIEO][BF₄] which was synthesizedby the polymer reaction shown in Scheme 3, were prepared by free radicalpolymerization of the ionic liquid monomers using AIBN as initiators.DMF was used as solvent because all poly(ionic liquid)s are soluble init. All these ionic liquid monomers are easily polymerized with highconversions. Poly(ionic liquid)s were precipitated in methanol to removeunreacted monomers. DMF residue in polymers was removed by drying at100° C. under vacuum. All poly(ionic liquid)s can dissolve in DMF, DMSO,acetonitrile, but are insoluble in water, dichloromethane and toluene.H¹ NMR and element analysis indicated the poly(ionic liquid)s were pure.

CO₂ Sorption and Desorption

The CO₂ sorption of the poly(ionic liquid)s was measured using a Cahn1000 Electrobalance. The sample pan and the counterweight of the balancewere configured symmetrically to minimize buoyancy effects. Themicrobalance has 100 g capacity and 1.0 μg sensitivity and is suitablefor study of sorption and diffusion of gases on/in solid or liquidmaterials. CO₂ gas (99.995%) was dried by passing two drying columns(length×diameter: 15 in×2 in) packed with P₂O₅. The fine powder of theionic liquid polymer was dried and degassed at 70° C. under vacuum for12 h to remove moisture or other volatile contaminants. It was furtherdried in the balance by evacuating the chamber at high vacuum until itsweight reached constant for at least 30 min. CO₂ was introduced into thechamber and the sample weight increase was recorded until the weight didnot change significantly in 30 min. The buoyancy effects in thesemeasurements were corrected according to the literature.²⁹ The systemwas validated by measuring the CO₂ sorption of an ionic liquid,1-n-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF₄]). Themeasured CO₂ sorption capacity of [bmim][BF₄] was identical to thereported.¹⁹

CO₂ has remarkable solubility in imidazolium-based ionic liquids becauseof its interactions with the anions and cations of ionic liquids.¹⁹ TheCO₂ sorption of (P[VBBI][BF₄] (a), P[VBBI][Tf₂N](b), P[MABI][BF₄] (c),P[VBBI] [Sac](d)), with their corresponding monomers ([VBBI][Tf₂N](e),[MABI][BF₄](g), [VBBI][BF₄](h), [VBBI][Sac](i)), and an ionic liquid[bmim][BE](f) as a function of time (592.3 mmHg CO₂, 22° C.) is shown inFIG. 1. The CO₂ solubility of [bmim][BF₄] was tested first and foundconsistent with that reported in the literature,¹⁹ which validated thesetup of the apparatus.

At the equilibrium, P[VBBI][BF₄], P[VBBI][Tf₂N], P[MABI][BF₄] andP[VBBI][Sac], respectively, took up 2.27 mol %, 2.23 mol % , 1.78 mol %and 1.55 mol % of CO₂ in terms of their monomer units. In comparison,room temperature ionic liquid [bmim][BF₄] absorbed 1.34 mol % of CO₂under the same conditions. [VBBI][BF₄] monomer had no measurablesorption of CO₂ because of its crystalline structure. [MABI][BF₄],[VBBI][Sac] and [VBBI][Tf₂N] monomers are liquid at room temperature.[MABI][BF₄] had the same CO₂ sorption capacity as [bmim][BF₄].[VBBI][Tf₂N] had a CO₂ sorption capacity of 1.96 mol %, higher than thatof [bmim][BF₄], which is consistent with the report that the ionicliquid with Tf₂N anions had higher capacity than ionic liquids with BF₄anions.¹⁴ [VBBI][Sac] did not take up any CO₂ when it was exposed to CO₂(FIG. 1). This comparison shows that polymerizing ionic liquids canincrease the CO₂ sorption capacity.

Meanwhile, the CO₂ sorption of the ploy(ionic liquid)s was much fasterthan that of ionic liquids. It takes only several minutes for thepoly(ionic liquid)s to reach their 90% capacity and less than 30 minutesto reach their equilibrium capacity. In contrast, room temperature ionicliquids [MABI][BF₄] and [bmim][BF₄] needed more than 400 min to reachtheir equilibrium capacity (FIG. 1).

The CO₂ sorption of poly(ionic liquid)s with different backbones,cations, and anions was compared to understand the factors affecting theCO₂ sorption. The CO₂ sorption kinetics of poly(ionic liquid)s withdifferent backbones are shown in FIG. 2. At the equilibrium, thepolymers sorbed 2.27 mol % (P[VBBI][BF₄]), 1.78 mol % (P[MABI][BF₄]) and1.06 mol % (P[BIEO][BF₄]), respectively, in terms of their monomer unitsat 592.3 mmHg of CO₂ and 22° C. With the same butylimidazolium cationand BF₄ ⁻ anion, the polymer with polystyrene backbone had a higher CO₂sorption capacity than those with polymethylmethacrylate andpolyethylene glycol backbones. The polymer with polyethylene glycolbackbone had the lowest capacity.

The effect of substituent of the imidazolium cation on the CO₂ sorptionis shown in FIG. 3. P[VBMI][BF₄], which has a methyl substituent on itsimidazolium cation, had a higher capacity (3.05 mol. %) thanP[VBBI][BF₄] (2.27 mol. %) with butyl group. This indicates that a largesubstituent on the imidazolium cation may block the CO₂ sorption.

The effect of the anions on the CO₂ sorption capacity of the poly(ionicliquid)s is shown in FIG. 4. The CO₂ sorption capacity the P[VBBI]-basedpolymers depends on the type of the anions: it was 2.80 mol. % forP[VBBI][PF₄], 2.27 mol % for P[VBBI][BF₄], 2.23 mol. % for P[VBBI][Tf₂N]and 1.55 mol. % for P[VBBI][Sac], respectively, in terms of theirmonomer units at 592.3 mmHg of CO₂ and 22° C. This trend is differentfrom that of ionic liquids. The CO₂ solubility in ionic liquids withTf₂N⁻ anions is much higher than those with PF₆ ⁻ or BF₄ ⁻ anions.¹⁹ Bycontrast, the poly(ionic liquid) with PF₆ ⁻ anions ([PVBBI][PF₆]) hadthe highest sorption capacity, and those with BF₄ ⁻ and Tf₂N⁻ anions hada similar capacity. The poly(ionic liquid) with Sac⁻ anions could takeup 1.55mol % of CO₂ even though the anion contains no fluorine atoms.These results indicate that for poly(ionic liquid)s, fluorine-atoms arenot a decisive factor for CO₂ sorption but fluorine-atoms in the anionsindeed enhance the CO₂ sorption.

The CO₂ sorption of the polymers is very selective, as shown in FIG. 5.There was no weight increase when the polymers were exposed to N₂ or 0₂under the same conditions, which means that poly(ionic liquid)s canselectively absorb CO₂.

The selective CO₂ sorption of the poly(ionic liquid)s was also confirmedby a gas-replacement experiment. The CO₂ sorption of P[VBBI][BF₄] (1gram) and desorption by replacing CO₂ with N₂ are shown in FIG. 6. Afterintroducing CO₂ into the balance, the sample weight increased rapidlyuntil it became constant after 12 min. The weight increase was 2.1 mg,and the actual weight increase was 3.10 mg after a buoyancy correction.When N₂ was introduced into the chambers while maintaining the totalpressure in the chambers at ambient pressure (592.3 mmHg), the sampleweight decreased gradually, and finally reached −0.56 mg, which wasequal to the buoyancy of the sample under N₂. This experiment indicatesthat the poly(ionic liquid) does not take up N₂. Similar experimentsconformed that there was no O₂ sorption.

The sorption isotherms of P[VBIM][BF₄] and P[BIMT][BF₄] at different CO₂partial pressures and 22° C. are shown in FIG. 7. The different CO₂partial pressures were obtained by adjusting the N₂/CO₂ ratio of themixed gas charged to the balance chambers because P[VBIM][BF₄] andP[MABI][BF₄] had no N₂ sorption. As shown in FIG. 7, the CO₂ molefraction in the polymers increased with the increase of CO₂ partialpressure.

Henry's constant is defined as

$H = {\lim\limits_{xarrow 0}\frac{p}{x}}$

where H is Henry's constant, x is the mole fraction of gas sorbed in thepolymer in term of monomeric unit, and P is the CO₂partial pressure.Since the x vs. P plots were not linear in the entire pressure range,Henry's constants were calculated by fitting the data and extrapolatingthe slope to the zero CO₂ partial pressure.¹⁶ Henry's constant was 26.0bar for P[VBBI][BF₄] and 37.7 bar for P[MABI][BF₄], which is lower thanthat of room temperature ionic liquid [bmim][PF₆] (38.7 bar at 10° C.and 53.4 bar at 25° C.).¹⁶

Stable sorption capacity after repeated sorption/desorption is importantfor materials used for CO₂ separation. Four cycles of CO₂ sorption anddesorption of P[VBBI][BF₄] and P[MABI][BF₄] were tested by filling thechambers with CO₂ and then vacuuming (FIG. 8 a). The sorption anddesorption of P[VBBI][BF₄] and P[MABI][BF₄] were all very fast. It tookonly about 30 min to take up CO₂ and to have a complete desorption ofCO₂. The desorption was complete, suggesting that thesorption/desorption was reversible. No change in sorption/desorptionkinetics and sorption capacity was observed after the four cycles. Bycontrast, the desorption of CO₂ from room temperature ionic liquids[bmim][BF₄] was very slow (FIG. 8 b)

The enhanced sorption capacity and fast sorption/desorption rates of thepoly(ionic liquid)s were unexpected because all polymers are solid atroom temperature. An immediate question is whether the sorption occurredon the surface (adsorption) or in the bulk (absorption) or both. The BETsurface area of P[VBBI][BF₄] was measured by nitrogen sorption and itsmorphology was examined by SEM. The measured BET surface area ofP[VBBI][BF₄] sample was 0.295 m²/g, The calculated CO₂-adsorptionassuming a monolayer of CO₂ on this surface was only 0.0128 wt %, muchless than the measured CO₂ sorption capacities. The SEM indicated thatthe particles had a nonporous structure, and the average diameter of theparticles was about 100 μm.

The CO₂ sorption of P[VBBI][BF₄] samples with different particle sizeswas tested (FIG. 10). The particle size did not significantly affect thecapacity of CO₂ sorption and the sample with a big size even had aslightly higher sorption capacity. However, the particle size affectedthe rate of CO₂ sorption. The CO₂ sorption of the sample with bigparticle sizes (>250 μm in diameter) was slow, and needed about 120minutes to reach its full sorption capacity, while those with theparticle diameters less than 125 μm in diameter only needed less than 30mins.

Without being bound to any particular theory, it appears that the CO₂sorption of the polymer particles involves more absorption (the bulk)but less adsorption (the surface). Their CO₂ sorption capacity mainlydepends on the chemical structure of poly(ionic liquid)s, while the rateof CO₂ sorption depends on the particle size due to the CO₂ diffusion inthe polymers.

EXAMPLE 2 Materials

4-vinylbenzyl chloride (90%), 1-methylimidazole (98%), lithiumtrifluoromethane sulfonimide 99.95%, potassium hexafluorophosphate 98%,sodium tetrafluoroborate (98%), 2, 6-Di-tert-butyl-4-methyl phenol (98%)(DBMP), N,N-Dimethylformamide (99.8%) (DMF), acetonitrile (99.5+%),acetone (99.5+%), aqueous [2-(methacryloyloxy)ethyl]rimethyl ammoniumchloride solution (75 wt. %), (p-vinylbenzyl)trimethylammonium chloride(98%), triethylamine (99.5%), tributylamine (99.5%) triphenylphosphine99%, α,α′-azobis(isobutyrobitrile)(AIBN) (98%) were purchased fromAldrich.1-methyl imidazole 99%, o-Benzoic sulphimide sodium salt hydrate(97%) were purchased from Lancaster Synthesis Inc. Pyridine waspurchased from Fisher scientific. All chemicals were used as received.

Synthesis and Characterization

(p-vinylbenzyl)trimethyl ammonium tetrafluoroborate ([VBTMA][BF₄]) and2-(methacryloyloxy)ethyltrimethylamnonium tetrafluoroborate([MATMA][BF₄]) were synthesized as described previously³⁰ using(p-vinylbenzyl)triethyl phosphonium tetrafluoroborate ([VBTEP][BF₄]),(p-vinylbenzyl)triphenyl phosphonium tetrafluoroborate ([VBTPP][BF₄]).

The synthesis of (p-vinylbenzyl)triphenyl phosphonium tetrafluoroborate([VBTPP][BF₄]), 1-(p-vinylbenzyl)pyridinium tetrafluoroborate([VBP][BF₄]) and 1-(p-vinylbenzyl)-3-methyl-imidazoliumtetrafluoroborate ([VBMI][BF₄]) is similar to1-(p-vinylbenzyl)-3-butyl-imidazolium tetrafluoroborate ([VBBI][BF₄])[VBBI][BF₄] (VBIT), as reported previously,²⁸ using triphenylphosphine,pyridine and 1-methyl imidazole instead of 1-butylimidazole,respectively.

The synthesis of (p-vinylbenzyl)triethylammonium tetrafluoroborate[VBTEA][BF₄] and (p-vinyl benzyl)tributylammonium tetrafluoroborate[VBTBA][BF₄] was follows: In a 50 ml flask, 4-vinylbenzyl chloride (6.1g, 0.04 mol) and triethylamine (4.2 g, 0.042 mol) mol were mixed andheated at 50° C. under N₂ atmosphere for 2 days. The formed solid waswashed with diethyl ether. The resultant white solid (8.5 g, 0.033 mol)was mixed with NaBF₄ (3.8 g, 0.035) in 50 acetonitrile and stirred atroom temperature for 2 days. The salt precipitate was removed byfiltration. The filtrate was concentrated and poured into 200 ml diethylether to precipitate out product. White crystal precipitate was formed,collected by filtration, and dried under vacuum. The total yield was 9.2g (75%). [VBTBA][BF₄] was synthesized according to a similar procedurewith yield of 64%.

In the synthesis of bis[(p-vinylbenzyl)dimethylammonium]ethane,[BVDEA][BF₄], which is an ionic liquid crosslinker,tetramethylethylenediamine (5.8 g, 0.05 mol), 4-vinylbenzyl chloride(16.0 g, 0.105 mol) and 0.1 g DBMP were mixed in 50 ml DMF. Theresulting solution was heated at 50° C. for 2 days. The solution waspoured into 400 ml diethyl ether to precipitate out the product. Afterfiltration and drying under vacuum, 15.8 g white crystal product wasobtained. The product was reacted with NaBF₄ (4.3 g, 0.04 mol) in 50 mldried acetonitrile for 2 days. After the reaction, the insolublechloride salt was removed by filtration. The product was collected byfiltration and dried under vacuum. The overall yield was 16.7 g (63.7%).

Poly(ionic liquid)s were synthesized by free radical polymerizationusing AIBN as initiator in DMF as described previously.³⁰ Thecrosslinked P[VBTMA][BF₄] was synthesized in the same way except foradding 5 wt % of the crosslinker.

The polymers were characterized by ¹H NMR on a Bruker Advance DRX-400spectrometer using d⁶-dimethylsulfoxide (DMSO-d⁶) as solvent. Theelemental analyses of polymers were tested by Midwest Microlab LLC (US).The CO₂ sorption of the poly(ionic liquid)s was measured using a Cahn1000 Electrobalance.

The structures of poly(ionic liquid)s are shown in Schemes 4 and 5. Twosteps were generally involved in the preparation of ionic liquidmonomers: the quaternization reaction and the anion exchange reaction ofthe halide ions with tetrafluoroborate, hexafluorophosphate, Sac or Tf₂Nanions. The resulting monomers are soluble in polar solvents, such asDMF, acetone, or acetonitrile. All monomers based on ammonium except forP[VBTMA][Tf₂N] are soluble in H₂O. The ionic liquid monomers based onphosphonium, pyridium, imidazolium are insoluble in H₂O. The poly(ionicliquid)s are soluble in DMF.

The ¹H NMR and elemental analyses indicated that the ionic liquidmonomers and poly(ionic liquid)s obtained were pure.

CO₂ Sorption and Desorption

FIG. 11 shows the effect of cation types on CO₂ sorption of poly(ionicliquid)s. The CO₂ sorption capacity of poly(ionic liquid)s withdifferent cations is as follows: P[VBTMA][BF₄] (10.2 mol. %)<P[VBTP][BF₄] (7.8 mol. %) <P[VBP][BF₄] (3.6%) <P[VBMI][BF₄] (3.0%). Thesolubility increases with increasing cation polarity. The polymer basedon ammonium has the highest solubility because of its highest cationpolarity. The polymer based on imidazolium, with the lowest cationpolarity, has the lowest solubility.

FIG. 12 shows the effect of anion types on the CO₂ solubility ofpoly(ionic liquid)s. The four polymers have the same cation structure,but different anions. P[VBTMA][PF₆] and P[VBTMA][BF₄] have a similar CO₂solubility of 10.7 mol. % and 10.2 mol. %, respectively. P[VBTMA][[Sac]and P[VBTMA][Tf₂N] have a solubility of 2.8 mol. % and 2.7%,respectively. The two poly(ionic liquid)s with inorganic anion have muchhigher solubility than the two with an organic anion, which can beexplained in terms of the anion polarity effect on the interactionbetween the poly(ionic liquid)s with CO₂; the higher the anion polarity,the higher the affinity to CO₂. As a result the poly(ionic liquid) withhigh anion polarity exhibit a higher CO₂ solubility.

The CO₂ sorption kinetics of poly(ionic liquid)s with differentbackbones are shown in FIG. 13. At the equilibrium, the polymers took up10.22 mol % (P[VBTMA][BF₄]), 7.99 mol % (P[MATMA][BF₄]), respectively,in terms of their monomer units at 592.3 mmHg of CO₂ and 22° C. With thesame ammonium cation and BF₄ ⁻ anion, the polymer with polystyrenebackbone had a higher CO₂ sorption capacity than that withpolymethylmethacrylate backbone.

The effect of substituent of the ammonium cation on the CO₂ sorption isshown in FIG. 14. Their CO₂ sorption capacities are as follows:P[VBTMA][BF₄] (10.2 mol. %) >P[VBTEA][BF₄] (4.85 mol. %) >P[VBTBA][BF₄](3.1 mol. %). Obviously, the CO₂ sorption capacity decreases withincreasing length of the substituent, which indicates that a largesubstituent on the ammonium cation blocks CO₂ sorption.

FIG. 15 shows the effect of crosslinking on CO₂ sorption of poly(ionicliquid). Compared with P[VBTMA][BF₄] without crosslinking, the CO₂sorption capacity of 5%-crosslinked P[VBTMA][BF₄] decreased by 17.3%.

EXAMPLE 3 Materials

Bis(2-hydroxyethyl)dimethyl ammonium chloride (Acros, 99%),2,2-Bis(bromomethyl)-1,3-propanediol (Aldrich, 98%), 1-Methylimidazole(Lancaster, 99%), 1-Butylimidazole (Aldrich, 98%),1,1-Carbonyldiimidazole (Aldrich, reagent grade), terephthaloyl chloride(Aldrich, 99+%), sodium tetrafluoroborate (Aldrich, 98%, NaBF₄),dimethyl sulfoxide (Aldrich, 99.9+%, DMSO) and methanol (A.C.S. reagent)were used as received. Acetonitrile (Aldrich, 99.5+%),N,N-Dimethylformamide (Aldrich, 99.8%, DMF) and triethylamine (EMD,99.5%, Et₃N) were used after removing water by molecular sieves.

Synthesis and Characterization

The synthesis of the monomers, Bis(2-hydroxyethyl)dimethyl ammoniumtetrafluoroborate ([BHEDMA][BF₄]) 1, 2,2-Bis(methylimidazoliummethyl)-1,3-propanediol tetrafluoroborate ([BMIMP][BF₄]) 2 and2,2-Bis(butylimidazolium methyl)-1,3-propanediol tetrafluoroborate([BBIMP][BF₄]) 3 is shown in Scheme 6. The reagents and conditions were:a) NaBF₄, acetonitrile, room temperature, 48 h, 96%; b)1-Methylimidazole, N₂, 60° C., 24 h, 98%; c) NaBF₄, acetonitrile, roomtemperature, 48 h, 96%; d) 1-Butylimidazole, N₂, 80° C., 24 h, 97%; d)NaBF₄, acetonitrile, room temperature, 48 h, 96%. Monomer 1 is anammonium-based ionic liquid, while 2 and 3 are imidazolium-based ionicliquids.

The synthesis of polycarbonate (PC) and polyethylene terephthalate (PET)types of ionic liquid polymers by condensation polymerization is asfollows. The PC type of ionic liquid polymers can be synthesized usingthe monomers 1 (2 or 3) reacted with 1,1-carbonyldiimidazole. The PETtype of ionic liquid polymers can be synthesized using the monomers 1 (2or 3) reacted with terephthaloyl chloride, respectively. Both kinds ofcondensation polymerizations required a strict 1:1 ratio of the reagentswith different difunctional groups. All the reactions were carried outin DMF at 60° C. for 24 h. All the polymers were precipiatated bymethanol after polymerization and dried under vacuum at 50° C.

The ionic liquid monomer 1 is colorless, while 2 and 3 have a lightyellow color. Synthesis of 2 and 3 in a N₂ atmosphere is necessarybecause the imidazole group is liable to be oxidized by the O₂ in theair, which will make the product have a brown color. For the1-methylimidazole is more active than 1-butylimidazole, it will reactwith 2,2-Bis(bromomethyl)-1,3-propanediol at a lower temperature (60°C.) than that of the 1-Butylimidazole (80° C.). All the monomers (1, 2and 3) are viscous liquids, and they all absorb moisture quickly whencontacting air, so all of them need to be dried in a rotating evaporatorbefore the polymerization.

The polycondensation synthesis of the PC type polymers,poly(bis(2-hydroxyethyl)dimethyl ammonium tetrafluoroborate) carbonate(P[BHEDMA][BF4]C) 4, poly(2,2-Bis(methylimidazoliummethyl)-1,3-propanediol tetrafluoroborate) carbonate (P[BMIMP][BF₄]C) 5,and poly(2,2-Bis(butylimidazolium methyl)-1,3-propanedioltetrafluoroborate) carbonate (P[BBIMP][BF₄]C) 6 is shown in Scheme 7.Polymer 4 is white, while 5 and 6 have a light yellow color. At roomtemperature, all polymers are easily crashed into fine powders. Polymer4 is soluble in acetonitrile, and polymer 5 and 6 are soluble inchloroform. They all can be cast into membranes for CO₂ separation usinga solvent evaporation method.

The synthesis of the PET type polymers, poly(Bis(2-hydroxyethyl)dimethylammonium tetrafluoroborate) terephthalate (P[BHEDMA][BF4]T) 7,poly(2,2-Bis(methylimidazolium methyl)-1,3-propanedioltetrafluoroborate) terephthalate (P[BMIMP][BF₄]T) 8 andpoly(2,2-Bis(butylimidazolium methyl)-1,3-propanediol tetrafluoroborate)terephthalate (P[BBIMP][BF₄]T) 9, is shown in Scheme 8. Triethylaminewas added to the reaction system slowly to remove the hydrogen chloride.The obtained three polymers (7, 8 and 9) are all white powders. But thesolubilities of them are not as good as those for the corresponding PCtypes because their phenyl groups increase the rigidity of the polymerchains greatly. Because they are only soluble in solvents with strongpolarity and high boiling points, such as DMSO and DMF, it is difficultto fabricate them into membranes using the solvent evaporation method.

EXAMPLE 4 Poly(Ionic Liquid) Membranes for CO₂/CH₄ and CO₂/N₂Separations

Poly(ionic liquid) grafted with polyethylene (PEG), for exampleP[VBTMA][BF₄]-g-PEG and P[MATMA][BF₄]-g-PEG [How were these “grafts”made?] were used to prepare membranes for CO₂/CH₄ and CO₂/N₂ separationsat 35° C., 50° C. and 70° C., all at 40 psig. These materials weretested for permeability and selectivity. FIG. 16 shows the CO₂/CH₄selectivity. FIG. 17 shows that our graft copolymers have betterproperties than the previously studied representative polymers forCO₂/CH₄ separation. FIG. 18 shows the selectivity of CO₂/N₂ for bothP[VBTMA][BF₄]-g-PEG and P[MATMA][BF₄]-g-PEG at 35° C., 50° C. and 70° C.FIG. 19 illustrates that both P[VBTMA][BF₄]-g-PEG andP[MATMA][BF₄]-g-PEG membranes exhibit better ideal separationperformance than the representative polymers because the data lie wellabove the upper limit bound curve, particularly for P[MATMA][BF₄]-g-PEG2000.

The foregoing description and drawings comprise illustrative embodimentsof the present inventions. The foregoing embodiments and the methodsdescribed herein may vary based on the ability, experience, andpreference of those skilled in the art. Merely listing the steps of themethod in a certain order does not constitute any limitation on theorder of the steps of the method. The foregoing description and drawingsmerely explain and illustrate the invention, and the invention is notlimited thereto, except insofar as the claims are so limited. Thoseskilled in the art who have the disclosure before them will be able tomake modifications and variations therein without departing from thescope of the invention.

REFERENCES

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We claim:
 1. A solid sorbent for separation of carbon dioxide from astream of mixed gases containing carbon dioxide, comprising a polymer ofa polymerized ionic liquid monomer wherein the ionic liquid is selectedfrom the group consisting of: (a) imidazolium-based ionic liquids,consisting of 1-[2-(methacryloyloxy)ethyl]-3-butyl-imidazoliumtetrafluoroborate ([MABI][BF₄]), 1-(p-vinylbenzyl)-3-butyl-imidazoliumtetrafluoroborate ([VBBI][BF_(4l)]),1-(p-vinylbenzyl)-3-methyl-imidazolium tetrafluoroborate [VBMI][BF₄],1-(p-vinylbenzyl)-3-butyl-imidazolium hexafluorophosphate [VBBI][PF₆],1-(p-vinylbenzyl)-3-butyl-imidazolium o-benzoic sulphimide([VBBI][Sac]), 1-(p-vinylbenzyl)-3-butyl-imidazolium trifluoromethanesulfonamide([VBBI][BF₄]), and (1-butylimidazolium-3)methyl-ethyleneoxide ([BIEO][BF₄]); (b) ammonium-based ionic liquids, consisting of(p-vinylbenzyl)trimethyl ammonium tetrafluoroborate ([VBTMA][BF₄]),(p-vinylbenzyl)triethyl ammonium tetrafluoroborate ([VBTEA][BF₄]),(p-vinylbenzyl)tributyl ammonium tetrafluoroborate ([VBTBA][BF₄]),2-(methacryloyloxy)ethyltrimethylamnonium tetrafluoroborate([MATMA][BF₄]), (p-vinylbenzyl)trimethyl ammonium hexafluorophosphate([VBTMA][PF₆]), (p-vinylbenzyl)trimethyl ammonium o-benzoic sulphimide([VBTMA][Sac]), and (p-vinylbenzyl)trimethyl ammonium trifluoromethanesulfonamide ([VBTMA][Tf₂N]); (c) phosphonium-based ionic liquids,consisting of (p-vinylbenzyl)triethyl phosphonium tetrafluoroborate([VBTEP][BF₄]), and (p-vinylbenzyl)triphenyl phosphoniumtetrafluoroborate ([VBTPP][BF₄]); (d) pyridinium-based ionic liquids,consisting of 1-(p-vinylbenzyl)pyridinium tetrafluoroborate ([VBP][BF₄])and (e) condensation polymerization ionic monomers, consisting ofbis(2-hydroxyethyl)dimethyl ammonium tetrafluoroborate ([BHEDMA][BF₄]),2,2-bis(methylimidazolium methyl)-1,3-propanediol tetrafluoroborate([BMIMP][BF₄]), and 2,2-bis(butylimidazolium methyl)-1,3-propanedioltetrafluoroborate ([BBIMP][BF₄]).
 2. A solid sorbent as defined in claim1, further comprising an inorganic moiety.
 3. A solid sorbent as definedin claim 1, further comprising a co-polymer.
 4. A solid sorbent asdefined in claim 1, wherein the polymerization is a polymerizationmethod selected from the group consisting of radical polymerization andcondensation polymerization.